In general, a method of sealing a wafer in an atmosphere of dry nitrogen gas or the like is employed for storing and transporting a semiconductor wafer. This storage method is carried out immediately after the wafer has been polished to form a mirror surface, or immediately after a distorted layer, a contaminated layer and the like are removed by an etching solution.
However, although bedewing and oxidation can be prevented to some extent by such a conventional method, a progression in the deterioration of the wafer surface caused by a residual polishing solution or by a residual etchant and a change in the surface stoichiometry caused by a difference in the vapor pressures or reactivities, which causes a problem in a semiconductor material of two or more elements such as GaAs, cannot be avoided.
Although any residual etchant or the like is removed by washing, the same still remains on the wafer surface in a thickness of about 1 atom by physical adsorption or chemical bond. Such a layer of the residual etchant or the like is so extremely thin that the same evaporates by an increase in temperature when of an epitaxial layer etc. is formed on the cleaned surface. No problem is caused when the residual etchant or the like is removed during the process of forming a device. However, the aforementioned evaporation is prevented if the residual etchant or the like has time to react with the surface of the semiconductor wafer to newly form a compound, leading to roughening of the surface.
In order to prevent such roughening of the surface, the wafer is generally treated by etching or the like immediately before the process of forming the epitaxial layer, etc. The steps of forming the device are complicated by such treatment, and hence the merit of improving the productive efficiency by high-volume processing cannot be achieved by conventional methods.